The invention concerns an extrusion device for tires.
The extrusion of tires, in particular, of car tires, is done in Europe--at least during the retreading--largely by the so-called bead-to-bead embodiment. In addition to the application of a new unvulcanized tread strip on the roughened outer surfaces, new sidewalls in the form of a calendered plate of 1 mm thickness are applied and stitched tight onto the flanks of the carcass, which are usually roughened by brushing only. In most cases, this embodiment requires the spraying of the brushed flanks with a rubber solution to provide assembly bonding of the new sidewall. The prepared carcass is then heated in the mold, wherein the tread design is molded into the tread strip and the company logo, tire size, and numbers representing the official tagging are molded into the sidewalls, followed by vulcanization.
The sidewall plate that has the required width and is provided on rolls having a cardboard core and an intermediate plastic layer, is practically applied to a slightly outwardly curved annular surface, resulting in a necessarily larger distance of the outer edge to the rotational axis of the tire than of the inner edge at the bead. Therefore, the plate must be pulled to a greater extent at the outside than at the inside. This is realized during manual application by means of special sidewall applicators and stitching machines.
When the plate is cut to length by a single cut, the required complete covering results in an at least triangular, or otherwise trapezoidal, overlapping at the "butt joint". If this overlap is not cut away by hand, the heating process in the mold results in a thicker portion. This is undesirable not so much because of balance error, but for visual reasons, i.e., selling considerations. Therefore, an additional cutting step of the butt joint is also unavoidable for automatic application devices, resulting in additional cost because of material waste in the form of the triangular or trapezoidal pieces of the sidewall plate and because of the manual labor requiring great care.
It is therefore an object of the invention to provide a retreading device that operates more cost-efficiently and eliminates, in particular, spraying of rubber solution onto the tire flanks that have been roughened by brushing.